Safe standby mode for ventilator

ABSTRACT

A ventilator with a safe standby mode is provided. The safe standby mode allows a user to disconnect a patient from the ventilator, without the ventilator generating alarms and while maintaining previously entered ventilation parameters. In addition, while in the safe standby mode, a patient connection status is monitored, and a ventilation mode is entered automatically if the ventilator determines that a patient is connected to the ventilator while the ventilator is in the safe standby mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/170,405, entitled “SAFE STANDBY MODE FORVENTILATOR,” filed on Jun. 1, 2016, which application is a continuationof U.S. patent application Ser. No. 13/618,359 (now U.S. Pat. No.9,381,314), filed on Sep. 14, 2012, which application is a continuationof U.S. patent application Ser. No. 12/236,127 (now U.S. Pat. No.8,424,520), filed on Sep. 23, 2008, the entire disclosures of which arehereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is generally directed to a safe standby mode for aventilator.

BACKGROUND

Ventilators are used to provide a breathing gas to a patient who isunable to breathe sufficiently without assistance. In modern medicalfacilities, pressurized air and oxygen sources are often available fromwall outlets. Accordingly, ventilators may provide pressure regulatingvalves connected to centralized sources of pressurized air andpressurized oxygen. The pressure regulating valves function to regulateflow so that respiratory air having a desired concentration of oxygen issupplied to the patient at desired pressures and rates. Ventilatorscapable of operating independently of external sources of pressurizedair and oxygen are also available.

A typical ventilator has a number of settings that can be used tocontrol parameters according to which breathing gas is supplied to apatient. In order to facilitate the entry of ventilator settings by auser, some ventilators have provided a standby mode. In a conventionalstandby mode, a user may set operating parameters, without breathing gasbeing provided at the supply port of the ventilator. Accordingly, inorder to provide breathing gas to a patient, the user must remember toexit the standby mode and enter a normal operating mode. If this is notdone, no benefit is provided to the patient, as no breathing gas issupplied in a conventional standby mode. Accordingly, such standby modesmay be considered unsafe, as the ventilator may appear to be on, eventhough no breathing gas is being supplied to the patient.

After ventilation of a patient has begun, a disconnect mode can beentered if the ventilator determines that the patient has becomedisconnected. In the disconnect mode, an alarm will typically sound ifthe disconnect state has persisted for some threshold period of time.Because of this, a medical professional may need to repeatedly silencethe disconnect alarm, for example while performing procedures thatrequire the disconnection of the patient from the ventilator. Moreover,in such situations, turning off the ventilator is not an attractiveoption, because there typically is a ventilator boot time or delaybetween powering on the ventilator and obtaining a breathing gas fromthe ventilator. In addition, patient settings will typically need to bereentered after the ventilator has been powered off. Although someventilators provide the option of entering a standby mode duringprocedures that require disconnecting the patient, the use of such aconventional standby mode is not particularly safe. In particular, nobreathing gas is supplied to the patient if the user forgets to restartnormal ventilation after entering the standby mode, even if the patientis connected to the ventilator.

SUMMARY

Ventilators with safe standby modes are provided. In some embodiments, aventilation mode providing breathing gas to a patient is entered inresponse to determining that the ventilator is connected to a patientwhile in the safe standby mode. In accordance with some embodiments ofthe present invention, the ventilator can also provide a prompt to auser that allows the user to select entry into the safe standby modeupon the ventilator determining that the patient has become disconnectedfrom the ventilator. In accordance with other embodiments of the presentinvention, a user may be offered an option of selecting a safe standbymode while the ventilator is in a normal ventilation mode.

More particularly, in response to detecting that a patient has becomedisconnected from the ventilator while the ventilator is in a normalventilation mode, the ventilator enters a disconnect mode. In thedisconnect mode, an alarm is periodically generated if the disconnectstatus is not resolved, for example by reconnecting the patient to theventilator or powering off the ventilator. In the disconnect mode,embodiments of the present invention allow the user to select the safestandby mode. In the safe standby mode, an alarm is not periodicallygenerated, and the ventilator may remain in the safe standby modeindefinitely. In addition, embodiments of the present invention monitora connection status of the patient while the ventilator is in the safestandby mode. If the ventilator determines that the patient has beenconnected to the ventilator while in a safe standby mode, a normalventilation mode in which breathing gas is supplied to the patient isentered automatically.

In accordance with further embodiments of the present invention, a usermay select the safe standby mode while the ventilator is in the normalventilation mode. In response to a selection of the safe standby mode,the ventilator may output a message to the user requesting that the userconfirm entry into the safe standby mode, and indicating that aspecified period of time will be allowed for completing patientdisconnection. After receiving confirmation from the user that the safestandby mode is to be entered, a countdown to the specified or definedperiod of time may be output. If the user completes patientdisconnection within the defined period of time, the safe standby modeis entered. After entering the standby mode, if the ventilator thendetermines that the patient has been reconnected to the ventilator,normal ventilation resumes. Also, if the user does not successfullydisconnect the patient within the defined period of time, normalventilation is continued. In accordance with further embodiments of thepresent invention, following a failure to disconnect the patient withinthe defined period of time, another opportunity to confirm entry intothe safe standby mode is presented, together with a notification of thedefined period of time in which disconnection will need to be completed.

Additional features and advantages of embodiments of the presentinvention will become more readily apparent from the followingdescription, particularly when taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a depiction of a ventilation system in accordance withembodiments of the present invention;

FIG. 2 is a block diagram depicting components of a ventilator providinga safe standby mode in accordance with embodiments of the presentinvention; and

FIGS. 3A-3B present a flow chart depicting aspects of the operation of aventilator providing a safe standby mode in accordance with embodimentsof the present invention.

DETAILED DESCRIPTION

FIG. 1 is a depiction of a ventilation system 100 in accordance withembodiments of the present invention. In general, the system 100includes a ventilator 104 connected to a patient circuit 108. Thepatient circuit includes an inspiratory limb 112, an expiratory limb116, and a patient limb 120. The inspiratory limb 112, expiratory limb116 and patient limb 120 are interconnected to one another by a patientwye 124. The inspiratory 112 and expiratory 116 limbs respectivelyconnect the patient wye 124 to a supply port 136 and a return port 140provided by the ventilator 104. The patient supply limb 120interconnects the patient wye 124 to a patient breathing apparatus 128.The ventilator 104 generally operates to provide a breathing gas to theinspiratory limb 112 for delivery to the patient breathing apparatus 128via the patient wye 124 and the patient supply branch 120. Theventilator 104 may also receive exhaled air from the patient that isdelivered to the return port 140 via the patient breathing apparatus128, the patient supply limb 120, the patient wye 124, and theexpiratory limb 116. The ventilator 104 may include a supply sensor 138and a return sensor 142 to monitor the supplied breathing gas and thereturned gas, respectively. Sensors 138 and 142 may be flow and/orpressure sensors, including flow or pressure transducers. In accordancewith embodiments of the present invention, information regarding theflow of gas detected by the supply 138 and return 142 flow transducersis provided to a controller 132.

In addition, the ventilator 104 includes user input 144 and user output148 facilities. In general, the user input 144 receives input from auser, such as a clinician, respiratory therapist, or other medicalprofessional, related to controlling the operation of the ventilator104. The user output 148 provides information to a user regarding theoperational status of the ventilator 104, and may include any alarmconditions.

The breathing gas supply 152 is operated at the direction of thecontroller 132, and includes the mechanical components used to controlthe composition and flow characteristics according to which breathinggas is supplied to a patient. In accordance with embodiments of thepresent invention, the breathing gas supply 152 is not limited to anyparticular type of breathing gas supply. Examples of a breathing gassupply 152 include piston and/or bellows based air delivery systems orair delivery systems comprising turbines. The breathing gas supply 152may additionally include pressure regulating valves. For example,pressure regulating valves may be used in connection with a mechanismfor compressing air included in the breathing gas supply 152, such as apiston or turbine. In accordance with other embodiments, the breathinggas supply 152 provides pressure regulating valves that are used tocontrol the flow of a gas or gasses provided by sources of pressurizedgas that are external to the ventilator 104, such as when the ventilator104 receives pressurized air and/or oxygen from centralized sourcesthrough wall outlets. In some embodiments, pressure regulating valvesinclude proportional solenoid valves.

Breathing gas from the breathing gas supply 152 may be provided to thepatient circuit 108 by the supply port 138. The supply flow sensor ortransducer 138 provides information regarding the flow of breathing gasthat is being output by the ventilator 104 through the supply port 136.This flow information is passed back to the controller 132, to providethe controller 132 with feedback regarding the flow actually providedfrom the supply port 136 of the ventilator 104 to a patient. The returnport flow sensor or transducer 142 monitors the flow of exhaled air froma patient that is received at the return port 140 of the ventilator 104.The information regarding the flow returned to the ventilator 104 fromthe patient circuit 108 is provided to the controller 132, which allowsthe controller 132 to perform various monitoring activities. Thesemonitoring activities can include detecting the connection status of apatient.

The user input 144 generally functions to receive control commands froma user regarding the operation of the ventilator 104. Accordingly, theuser input 144 can include one or more devices, such as a keyboard, anumeric keypad, a pointing device operated in connection with a displaydevice, a touch screen interface and/or a microphone for receivingspoken commands. The user input 144 may additionally or alternativelyinclude buttons or switches, either physical or virtual, that arededicated to the control of specific ventilator 104 functions.

The user output 148 may comprise one or more devices that are operableto providing human perceptible output signals. Accordingly, examples ofuser output devices 148 include visual displays, indicator lamps, oraudible signals. In addition, a user output 148 may include a deviceprovided separately from or external to the ventilator 104. Forinstance, the user output 148 may comprise a communication interfaceprovided as part of the ventilator 104 that provides a signal that iscommunicated to a user communication endpoint, such as a cellulartelephone, pager or personal computer that causes the user endpoint toprovide a human perceptible signal.

FIG. 2 is a block diagram depicting components of a ventilator 104 thatprovides a safe standby mode in accordance with embodiments of thepresent invention. As shown in FIG. 2, the ventilator 104 controller 132may comprise a number of separate or integrated components. Thesecomponents may include a processor 204 that is operable to executeprogram code, instructions or firmware related to the operation of theventilator 104. The processor 204 may therefore comprise a generalpurpose programmable processor, an application specific integratedcircuit or other processor. The code or instructions executed by theprocessor 204 may be stored in memory 208. The memory 208 generallycomprises one or more solid state memory devices. Alternatively or inaddition, the memory 208 may include other types of data storagedevices, such as magnetic or optical storage devices. In general, atleast some of the memory 208 is non-volatile, to allow for the long termstorage of operating instructions for execution by the processor 204.Such instructions may include a ventilation control application 212. Inaddition, the memory 208 may be used to store user settings 216, forexample entered in connection with use of the ventilator 104 to providebreathing gas to a particular patient.

The ventilation control application 212 generally controls the operationof the ventilator 104 in providing a breathing gas to a patient.Accordingly, this may include controlling the breathing gas supply 152such that breathing gas having desired composition and flowcharacteristics is provided to the patient. In addition, the ventilationcontrol application 212 may implement various sub-functions of theventilator 104, such as a patient connect/disconnect detection function220, a safe standby mode function 224, and the implementation of one ormore timers 228 that may be set and monitored in connection with theexecution of other functions. The user settings 216 generally includeoperating parameters entered by a user that relate to controlling thecomposition and flow characteristics of the breathing gas supplied to apatient, and any other user configurable operating parameters.

The controller 132 may also include one or more input/output interfaces232. The input/output interfaces 232 operatively connect the controller132 to other components of the ventilator 104. Accordingly, examples ofinput/output interfaces 232 may include communication bus or networkinterfaces, and/or dedicated input or output signal lines. In accordancewith embodiments of the present invention, the controller 132 may beprovided as a set of discrete components. Alternatively, the controller132 may comprise a fully or partially integrated controller device.

In accordance with embodiments of the present invention, the user input144 and user output 148 may operate in association with the ventilationcontrol application 212 executed by or running on the processor 204 toprovide a graphical user interface (GUI). Accordingly, a user mayinteract with the ventilator 104 by making selections and receivinginformation through a GUI provided by the ventilator 104. Alternativelyor in addition, dedicated control inputs and outputs, such as switches,buttons, indicator lamps and audible alarms may be provided.

FIGS. 3A and 3B provide a flow chart depicting aspects of the operationof a ventilator 104 with a safe standby mode in accordance withembodiments of the present invention. Starting at step 300, ventilationof a patient is initiated. While the patient is being ventilated, thecontroller 132 may monitor the patient circuit 108 to determine whetherthe patient has become disconnected from the ventilator 104 (step 304).If it is determined that the patient has become disconnected from theventilator 104, a disconnect mode is entered, and the user is promptedto select a safe standby mode or to cancel (step 308). For example, thefollowing message may be displayed by the GUI of the ventilator 104:

-   -   Do you want to enable SAFE STANDBY?    -   [YES] [CANCEL]        At step 312, a determination as to whether a safe standby mode        has been selected. If the safe standby mode has not been        selected, a determination is made as to whether the “cancel”        button has been selected (step 314). If “cancel” has been        selected, the normal ventilation mode is resumed (step 318), and        the process returns to step 304.

If “cancel” is not selected, the disconnect mode is continued (step316). In the disconnect mode, the ventilator 104 does not providebreathing gas through the supply port 136 with the flow characteristicsapplied while in the ventilation mode. Instead, gas is supplied at agreatly reduced rate. As can be appreciated by one of skill in the art,by providing gas at a reduced rate through the supply port 136, thechance that microorganisms or other dangerous substances might beaerosolized and sprayed out of the patient circuit 108 is reduced. Forexample, whereas the ventilator 104 might supply breathing gas at flowsof one hundred and fifty to two hundred (150-200) liters per minuteduring normal ventilation, in the disconnect mode gas is supplied at arate of three (3) liters per minute. Providing some gas, even at areduced flow, allows the ventilator 104 to monitor whether the patienthas been reconnected. In particular, if a flow (or certain pressure) isdetected at the return port 140 by the return port transducer 142, itmay be taken as an indication that a patient has been reconnected, andnormal ventilation may resume. Accordingly, while the ventilator 104 isin the disconnect mode, a check may be performed continually todetermine whether the disconnect status has been resolved by connectinga patient to the ventilator (step 320). If it is determined that apatient has been connected to the ventilator 104, the normal ventilatormode is resumed (step 318).

If a connection to the patient is not detected at step 320, adetermination may be made as to whether the period of time that theventilator 104 has been in the disconnect mode exceeds some thresholdperiod (step 324). As an example, the threshold period may be defined orselected to be five (5) seconds. If the threshold period of time hasbeen exceeded, a high priority disconnect alarm is generated (step 328).After generating the alarm or after determining that the thresholdperiod of time has not been exceeded, the process may return to step312.

If it is determined at step 312 that a safe standby mode has beenselected, the safe standby mode is entered (step 332). In the safestandby mode, the ventilator 104 is powered on and all settings enteredby the user are maintained. However, in the safe standby mode breathinggas is not supplied at normal rates of ventilation. Instead, gas isdelivered from the supply port 138 at reduced rates in order to monitorwhether a patient is connected to the ventilator 104 while theventilator 104 is in the safe standby mode. That is, the same techniquesthat are used to determine whether a patient has been connected to theventilator in the disconnect mode are used in the safe standby mode.However, the safe standby mode differs from the disconnect mode in thata disconnect alarm is not periodically generated. Therefore, the patientcan remain disconnected from the ventilator indefinitely, withoutrequiring the user to periodically take action to silence a disconnectalarm. At step 336, a determination is made as to whether a patientconnection to the ventilator 104 has been detected. If the monitoringdetermines that the patient remains disconnected, monitoring for aconnection to a patient is continued. If a connection to a patient isdetected, the normal ventilation mode is resumed (step 340). When thenormal ventilation mode is resumed, ventilation of the patient may beperformed in accordance with the parameters previously set by the user.

As can be appreciated by the description provided herein, the safestandby mode provided by some embodiments of the present inventionautomatically resumes the supply of a breathing gas according topreviously selected flow characteristics if the ventilator 104 detectsthat the patient has been reconnected to the ventilator 104. This is incontrast to conventional ventilator standby modes, in which no automaticrestart of ventilation is provided if the patient is reconnected to theventilator. In addition, no disconnect alarm is sounded in the safestandby mode of embodiments of the present invention.

In some embodiments, after ventilation of the patient has been resumedat step 340, or if a patient disconnect has not been detected at 304, adetermination may be made as to whether a selection of the safe standbymode has been received from a user while the ventilator 104 is in thenormal ventilation mode (step 344) (see FIG. 3B). A safe standby modecan be selected by a user through, for example, a menu selection enteredthrough the ventilator graphical user interface. If a selection of thesafe standby mode has been received, the user is prompted by theventilator 104 to confirm or cancel the safe standby mode selection(step 348). For example, the following message may be displayed by theGUI of the ventilator 104:

-   -   Do you want to enable SAFE STANDBY?    -   (You will have 5 seconds to disconnect patient)    -   [YES] [CANCEL]

A determination is then made as to whether the user has confirmed orcanceled the safe standby mode selection (step 352). If the user selectsYES to confirm, the ventilator 104 will display a countdown) (step 356).A determination is then made as to whether a patient disconnect has beendetected within the countdown period (step 360). The countdown periodmay be a set period of time, for example, five (5) seconds, seven (7)seconds, ten (10) seconds, or the like. In alternative embodiments, theduration of the countdown period may be based on the respiration rate.For example, the countdown may last for a period of time equal to onefull breath, two full breaths, or the like. Other methods ofestablishing a desired countdown period are possible within the scope ofthe present invention. As described previously, detection of a patientconnection to the ventilator may be performed by monitoring whether areturn flow is sensed by the return flow transducer 142 of theventilator 104. If a patient disconnect is not detected within thecountdown period, ventilation of the patient is continued (step 364). Inaddition, a low priority alarm may be generated, and/or the user may befurther prompted to confirm or cancel the safe standby mode (step 368).For example, the following may be displayed by the ventilator GUI:

-   -   Patient Disconnect has taken too long    -   Do you still want to enable SAFE STANDBY?    -   (You will have 5 seconds to disconnect patient)    -   [YES] [CANCEL]        The process may then return to step 352 to determine whether the        user has confirmed or canceled the safe standby mode selection.        In accordance with embodiments of the present invention,        ventilation of the patient is also continued if a selection of a        safe standby mode is not received while the ventilator 104 is in        the ventilation mode, or if the user fails to confirm a        selection of the safe standby mode.

If it is determined at step 360 that the patient has been disconnectedwithin the countdown period, the process proceeds to step 332, in whichthe safe standby ode is entered.

If it is determined at step 352 that the user has not confirmed entryinto the safe standby mode, a determination may be made as to whetherthe user has canceled the safe standby mode selection (step 370). If theselection of the safe standby mode has been canceled, the processproceeds to step 318, and normal ventilation is resumed. If the user hasnot canceled the selection of the safe standby mode, a determination maybe made as to whether a threshold time period since the user wasprompted to confirm or cancel the safe standby mode exceeds somethreshold amount (step 372). If the threshold time period has elapsedwithout receiving an entry from the user, normal ventilation may beresumed (step 318). If the threshold time has not been exceeded, theprocess may return to step 352 to monitor for a user selection.

In addition, a user may choose to discontinue ventilation at any time.If ventilation has not been discontinued, the process may return to step304. If ventilation has been discontinued the process may end. Also,although processes that may be performed by a ventilator in accordancewith embodiments of the present invention have been described inconnection with steps that are performed in series, it should beappreciated that embodiments of the present invention are not limited tolinear or serial operations. For example, the ventilator 104 maycontinuously monitor for any of a plurality of inputs from a user, forpatient disconnect status, and/or for other inputs or conditions.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. Further, the description isnot intended to limit the invention to the form disclosed herein.Consequently, variations and modifications commensurate with the aboveteachings, within the skill or knowledge of the relevant art, are withinthe scope of the present invention. The embodiments describedhereinabove are further intended to explain the best mode presentlyknown of practicing the invention and to enable others skilled in theart to utilize the invention in such or in other embodiments and withvarious modifications required by the particular application or use ofthe invention. It is intended that the appended claims be construed toinclude alternative embodiments to the extent permitted by the priorart.

What is claimed is:
 1. A ventilator comprising: a processor; and amemory storing computer-readable instructions that when executed by theprocessor cause the ventilator to: deliver ventilation to a patientaccording to a normal mode of ventilation; receive an indication toinitiate a standby mode of ventilation; receive a confirmation of theindication to initiate the standby mode of ventilation; disable at leastone patient disconnect alarm; monitor for disconnection of the patientfrom the ventilator; when disconnection of the patient occurs within aperiod of time, discontinue ventilation to the patient according to thenormal mode of ventilation.
 2. The ventilator of claim 1, thecomputer-readable instructions when executed by the processor furthercausing the ventilator to: monitor for reconnection of the patient tothe ventilator.
 3. The ventilator of claim 2, the computer-readableinstructions when executed by the processor further causing theventilator to: in response to detecting reconnection of the patient tothe ventilator, automatically resume the ventilation to the patientaccording to the normal mode of ventilation.
 4. The ventilator of claim3, the computer-readable instructions when executed by the processorfurther causing the ventilator to: store ventilator settings for use inthe normal mode of ventilation; and automatically resume the normal modeof ventilation based on the stored ventilator settings.
 5. Theventilator of claim 1, the computer-readable instructions when executedby the processor further causing the ventilator to: deliver gases at areduced rate during the standby mode of ventilation.
 6. The ventilatorof claim 5, wherein delivering the gases at the reduced rate enables theventilator to detect reconnection of the patient to the ventilator. 7.The ventilator of claim 1, the computer-readable instructions whenexecuted by the processor further causing the ventilator to: whendisconnection of the patient does not occur within the period of time,continue ventilation to the patient according to the normal mode ofventilation.
 8. The ventilator of claim 1, the computer-readableinstructions when executed by the processor further causing theventilator to: provide a prompt for receiving confirmation of theindication to initiate the standby mode of ventilation.
 9. A methodimplemented by a ventilator, the method comprising: receiving anindication to initiate a standby mode of ventilation; receiving aconfirmation of the indication to initiate the standby mode ofventilation; disabling at least one patient disconnect alarm; monitoringfor disconnection of the patient from the ventilator; when disconnectionof the patient occurs within a period of time, discontinuing ventilationto the patient according to a normal mode of ventilation.
 10. The methodof claim 9, further comprising: monitoring for reconnection of thepatient to the ventilator.
 11. The method of claim 10, furthercomprising: in response to detecting reconnection of the patient to theventilator, automatically resuming ventilation to the patient accordingto the normal mode of ventilation.
 12. The method of claim 11, furthercomprising: storing ventilator settings for use in the normal mode ofventilation; and automatically resuming the normal mode of ventilationbased on the stored ventilator settings.
 13. The method of claim 9,further comprising: delivering gases at a reduced rate during thestandby mode of ventilation.
 14. The method of claim 13, whereindelivering the gases at the reduced rate enables the ventilator todetect reconnection of the patient to the ventilator.
 15. The method ofclaim 9, further comprising: when disconnection of the patient does notoccur within the period of time, continue ventilation to the patientaccording to the normal mode of ventilation.
 16. The method of claim 9,further comprising: providing a prompt for receiving confirmation of theindication to initiate the standby mode of ventilation.
 17. A ventilatorcomprising: a processor; and a memory storing computer-readableinstructions that when executed by the processor cause the ventilatorto: deliver ventilation to a patient according to a normal mode ofventilation; receive an indication to initiate a standby mode ofventilation; receive a confirmation of the indication to initiate thestandby mode of ventilation; disable at least one patient disconnectalarm; monitor for disconnection of the patient from the ventilator; inresponse to determining whether disconnection of the patient occurswithin a period of time, perform one of: discontinue ventilation to thepatient according to the normal mode of ventilation; or continueventilation to the patient according to the normal mode of ventilation.18. The ventilator of claim 17, when disconnection of the patientoccurred within the period of time, the computer-readable instructionswhen executed by the processor further causing the ventilator to:monitor for reconnection of the patient to the ventilator.
 19. Theventilator of claim 18, the computer-readable instructions when executedby the processor further causing the ventilator to: in response todetecting reconnection of the patient to the ventilator, automaticallyresume the ventilation to the patient according to the normal mode ofventilation.
 20. The ventilator of claim 17, the computer-readableinstructions when executed by the processor further causing theventilator to: deliver gases at a reduced rate during the standby modeof ventilation.
 21. The ventilator of claim 20, wherein delivering thegases at the reduced rate enables the ventilator to detect reconnectionof the patient to the ventilator.